1. Field of the Invention
This invention deals with micromechanical devices, more particularly with micromechanical deformable mirror devices.
2. Description of the Prior Art
There are many different types of micromechanical devices, three of which are micro-motors, micro-gears, and micromechanical deformable mirror devices (DMD). Micromechanical DMDs contain an activation or addressing electrode, a support post or posts, underneath a hinge or hinges, which in turn supports a deflection element suspended over the electrode. The DMDs are primarily used in the direction of light in optical systems, with a mirrored deflection element.
The operation of such devices involves activating the electrode which builds up electrostatic charge in the gap between electrode and deflection element. The deflection element then flexes on its hinge or hinges and moves towards the electrode. When the charge is removed, the deflection element returns to its undeflected position.
Contact between the operating and supporting pieces of micromechanical devices such as micro-gears and micro-motors may result in sticking. Likewise, if the deflection element of a DMD comes into contact with the electrode, it may possibly stick in the deflected position. One method of freeing the deflection element of a DMD is by the application of a voltage pulse train with a frequency around the resonant frequency of the hinge. When the pulse train ceases, the deflection element returns to its undeflected position.
This method of reset works very well. However, after many contacts between electrode and deflection element, the wear increases the effective contact area. This requires higher and higher voltages for reset.